Bi-directional inverter-charger

ABSTRACT

A bi-directional inverter-charger including a bridge rectifier and DC-to-DC conversion components. The inverter-charger may be connected between an alternating current source, e.g., an AC line, and a direct current source, e.g., a battery pack. The DC-to-DC conversion components may include boost and buck circuits that are switchably configured between a charge mode and an inverter mode such that common components are used in both charge and inverter configurations. In the charge configuration, a full wave rectified signal from the H-bridge is up converted by the boost circuit, and the buck circuit controls charge current to the direct current source. In the inverter configuration, the boost circuit up converts the direct current voltage source, and the buck circuit controls the current and its form to the bridge circuit so that the bridge circuit may be Connected directly with the AC source.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application claiming priorityunder 35 U.S.C. §120 to utility application Ser. No. 12/558,458 titled“Bi-Directional Inverter-Charger” filed on Sep. 11, 2009, which claimspriority under 35 U.S.C. §119 (e) to provisional application No.61/096,311 titled “Bi-directional Inverter-Charger System,” filed onSep. 11, 2008, which are hereby incorporated by reference herein.

FIELD OF THE INVENTION

Aspects of the present invention generally relate to a bi-directionalinverter-charger system.

BACKGROUND

Products for converting alternating current (AC) to direct current (DC)are commonly found in the marketplace today. These products, when usedto move electrical energy into a battery, are referred to as chargers.Products that convert DC into AC are referred to as inverters.

Hybrid-Electric Vehicles or “HEV”'s have both an electric drive trainand a gasoline or other form of combustion engine. While variousspecific HEV configurations are possible, generally speaking, theelectric motor may drive the vehicle, drawing energy from a battery packalone or in combination with the combustion engine may also power agenerator that charges the battery pack. One problem with many existingmass produced HEVs is that the full potential of the hybrid drive systemis not realized due to the limited amount of on-board electrical energystorage. This problem is addressed by increasing the energy storagecapacity of the vehicle to allow greater use of electricity in place ofgasoline, which is being facilitated by technical advances in battery orother energy storage forms, among other things. Higher capacity energystorage systems facilitate charging from an external supply to offsetand reduce petroleum fuel consumption that would otherwise be requiredby the petroleum fueled engine. Such a configuration is known as aPlug-in Hybrid Electric Vehicle or PHEV.

Now consider that PHEVs often now have a large capacity battery forelectrical energy storage but that stored energy is used only when thevehicle is moving. When the vehicle is at rest the battery system isidle and underutilized. It has been recognized that the energy storagecapacity of PHEVs could be utilized to store electrical energy when thepower is available and it could be called upon to supply electricalenergy when required during times of peak electric grid demand—a conceptreferred to as Vehicle-To-Grid or V2G.

SUMMARY

With a developing interest in V2G technologies, as well as V2H(vehicle-to-home), V2V (vehicle-to-vehicle) and other technologies whereenergy flows between differing sources, bidirectional inverter-chargersystems are needed, among many other things. Aspects of the presentinvention involve a bi-directional topology using a single synchronousbridge rectifier or unfolder. The bi-directional inverter-chargerprovides both AC-to-DC conversion for charging a storage source, such asa battery pack, and DC-to-AC inversion for connecting the battery to thegrid or other AC voltage source. This allows for the same powercomponents to be used in both directions resulting in high energytransfer efficiency with fewer components.

Aspects of the present disclosure involve an inverter charger forproviding a bidirectional energy flow between an alternating currentsource and a direct current chargeable voltage source. The invertercharger may include an H-bridge rectifier inverter circuit coupled withan alternating current voltage source. The inverter charger may furtherinclude a direct current voltage to direct current voltage converter(DC-to-DC converter) coupled between the H-bridge inverter circuit and adirect current chargeable voltage source having a direct currentvoltage, the DC-to-DC converter switchable between a chargeconfiguration and an inverter configuration. The DC-to-DC converter,switched to charge configuration, includes a boost circuit operablycoupled with the H-bridge. The H-bridge rectifier provides a full waverectified output signal to the boost circuit. The boost circuit isconfigured to up convert the full wave rectified output signal. In thecharge configuration, the DC-to-DC converter further includes a buckcircuit operably coupled with the boost circuit. The buck circuit isconfigured to provide a regulated charge current to the direct currentchargeable voltage source. The inverter charger, in inverterconfiguration, includes the boost circuit operably coupled with thedirect current chargeable voltage source. The boost circuit isconfigured to up convert the direct current voltage of the directcurrent chargeable voltage source, and the buck circuit is configured toprovide a full wave rectified signal wave form to the H-bridge. TheH-bridge is configured to tie an alternating current voltage waveform tothe alternating current voltage source. While the application generallyrefers to an alternating current source, it should be appreciated thatit may also be a load.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a bi-directional inverter-chargercoupled between an AC line and a battery pack;

FIG. 2 is a block diagram illustrating one possible implementation of abi-directional inverter-charger;

FIG. 3 is an electrical schematic of one possible implementation of abi-directional inverter-charger configured for charging a battery pack;

FIG. 3A is a diagram of one possible power MOSFET that may be used toimplement various switches discussed herein;

FIG. 4A is a voltage waveform for a 240 VAC (RMS) AC line, which may beconnected with a bi-directional inverter-charger to charge a battery orotherwise provide charge current to a DC source conforming to aspects ofthe present disclosure;

FIGS. 4B-4E are voltage waveforms of control signals that may be used tocontrol operation of switches employed in an H-bridge portion of abi-directional inverter-charger conforming to aspects of the presentdisclosure;

FIG. 4F is a voltage waveform for a rectified AC signal from an H-bridgeportion of a bi-directional inverter-charger conforming to aspects ofthe present disclosure;

FIG. 5 is a control diagram for a boost circuit forming a portion of aDC-to-DC portion of a bi-directional inverter-charger conforming toaspects of the present disclosure;

FIG. 6A is a voltage waveform for the output of a boost circuit portionof a DC-to-DC portion of a bi-directional inverter-charger conforming toaspects of the present disclosure;

FIG. 6B is a current waveform for an inductor of a boost circuit portionof a DC-to-DC portion of a bi-directional inverter-charger conforming toaspects of the present disclosure;

FIG. 6C is a voltage waveform for an inductor of a boost circuit portionof a DC-to-DC portion of a bi-directional inverter-charger conforming toaspects of the present disclosure;

FIG. 6D is a voltage waveform across a switch of a boost circuit portionof a DC-to-DC portion of a bi-directional inverter-charger conforming toaspects of the present disclosure;

FIG. 6E is a PWM control signal for a switch of a boost circuit portionof a DC-to-DC portion of a bi-directional inverter-charger conforming toaspects of the present disclosure;

FIG. 7 is a charge current control diagram for a buck circuit forming aportion of a DC-to-DC portion of a bi-directional inverter-chargerconforming to aspects of the present disclosure;

FIG. 8 is an electrical schematic of one possible implementation of abi-directional inverter-charger configured for tying a battery pack to agrid or other load/source;

FIG. 9 is a grid tie control diagram for a buck circuit forming aportion of a DC-to-DC portion of a bi-directional inverter-chargerconforming to aspects of the present disclosure;

FIG. 10A is a output voltage waveform for a buck circuit connected withan H-bridge in a grid tie (discharge/inverter) configuration of oneexample of a bi-direction inverter-charger;

FIG. 10B is a output current waveform for a buck circuit connected withan H-bridge in a grid tie (discharge/inverter) configuration of oneexample of a bi-direction inverter-charger;

FIG. 10C is a voltage waveform for a 240 VAC (RMS) AC line, which may beconnected to in a grid tie arrangement with a bi-directionalinverter-charger conforming to aspects of the present disclosure; and

FIG. 11 is a schematic diagram of one possible arrangements of relays toprovide for switching between charge and inverter modes of abi-directional inverter-charger.

DETAILED DESCRIPTION

Aspects of the invention involve an inverter-charger system that usescommon components for both inverter and charger functions. In oneapplication, the inverter-charger is employed in a plug-in hybridelectric vehicle or electric vehicle application, internal or externalto the vehicle, and provides for charging a vehicle battery or otherrechargeable energy storage device and also allows the battery to beconnected to an electric power grid or otherwise and deliver power tothe grid. In charger mode, the inverter-charger is coupled with analternating current (AC) power source, such as a conventional 120V or240V wall outlet, and the AC power is converted to direct current (DC)for charging the battery coupled with the inverter-charger. In invertermode, the same inverter-charger reverses the flow of energy and convertsDC power from the battery to AC power and provides the AC power to thegrid. Hence, by employing an inverter-charger system as discussedherein, the vehicle battery may act as energy source for use in poweringthe vehicle and may also act as an energy source to deliver energy tothe grid, a home, or otherwise for other uses.

FIG. 1 is a high level block diagram of one example of inverter-chargersystem 10 as might be used to control the flow of electrical energy 12in a vehicle-to-grid, vehicle-to-home, or other application. Theinverter-charger is functionally positioned between a battery pack 14 ofa vehicle and an alternating current supply 16. The battery pack mayhave a direct current voltage of between 150 and 380 volts; however, theinverter-charger may be used with packs having other voltages, whetherhigher or lower than the examples used herein. The various battery packvoltage examples used herein are often nominal or peak, and may be lowerwhen in a discharged state or higher during charging. The alternatingcurrent supply in the system example of FIG. 1 is an alternating currentline voltage of between 100 volts and 240 volts at 60 Hz (single phase),with typical residential U.S. line voltages being 120 VAC or 240 VAC.The inverter-charger may be configured to couple with other alternatingcurrent voltage levels. “Charging” is the term that describes when thesystem is configured to convert the alternating current from the line todirect current to charge the battery pack 14. “Inverting” is the termthat describes when the system is configured to convert the directcurrent voltage from the battery pack to alternating current in order tocouple the battery pack to the grid or other source. The invertercharger can also be configured to provide AC energy to power loads orused as an emergency or auxiliary power source.

The inverter-charger system is discussed herein within the context of aplug-in hybrid or electric vehicle having a battery pack and aconventional alternating current line voltage. The inverter-charger,however, may be deployed in other systems where bi-directional couplingbetween a high voltage AC and high voltage DC energy storage/suppliesare required. For example, the AC supply may be provided from a windturbine array. In such an example, it is quite possible that the batterymay be used for energy storage when energy from the turbine is notavailable (not windy). For example, in a facility, whether a home orotherwise, with a wind turbine providing power to the facilities energygrid, the plug-in hybrid battery may be tied to the grid and be charged.When the turbine is not delivering energy, the battery may be used toprovide grid energy for the home's power needs. Further, numerous suchpossible uses will evolve as smart grid and other such technologies aredeveloped and deployed.

FIG. 2 is a block diagram of one example of an inverter-charger system10. As introduced in FIG. 1, the inverter-charger is functionallypositioned between the battery pack or other storage system 14 and aline voltage or other supply voltage 16. In the energy path 12 betweenthe battery and line, there is a rectifier/inverter (or bridge) 20 andDC-DC conversion components 30. Configured as a charger, the rectifierconverts the AC line voltage to a full-wave rectified DC voltage. Fromthe rectified DC voltage, the DC-DC converters 30 then provide theproper charge current at the proper DC voltage to the battery pack 14.Configured as an inverter, the DC-DC converters up convert the DCbattery pack voltage to an appropriate voltage level for the inverter 20to convert the DC voltage to an AC line voltage, sufficient to deliverpower, and at the proper frequency.

The system 10 may be advantageously configured to use the sameinverter/rectifier 20 and DC-DC converters 30 in both the charging andinverting modes, which is accomplished through DC relays 28, solid stateswitches, or other switch mechanisms. The DC relays, under programmaticcontrol of a controller 22, are configured to alter the energy flow pathbetween the battery 14, appropriate DC converter components 30, and thebridge 20. While AC relays 24, also under programmatic control of thecontroller 22, are shown connecting the bridge 20 to the line 16 duringboth charging and inverting, the implementations discussed herein do notinclude AC relays.

FIG. 3 is a circuit diagram of one example of an inverter-charger 10configured for charging. Discussing the circuit from right to left, i.e.from the AC source 16 to the battery 14, the inverter-charger 10includes a line filter 34 connected to the source 16. The line filter isa conventional line filter comprising two capacitors (C1 and C2) inparallel with the source 16, and an inductor L1 in series with thesource and connected between each capacitor. The line filter attenuatesor otherwise reduces electromagnetic interference between the line 16and the inverter-charger. The line filter shown is but one example offilter configurations that might be employed in various implementationsconforming to the present disclosure.

A rectifier 20 is coupled with the line filter. The rectifier includesfour transistor switch configurations MI-M4 arranged as an H-bridge. TheH-bridge configuration allows for bidirectional energy flow through thecircuit. Hence, with the H-bridge under programmatic control, thecircuit may be operated as a full wave rectifier in charge mode and asan inverter in the inverter grid tie or auxiliary source discharge mode.

In one particular implementation, each switch M comprises threen-junction power MOSFETS connected in parallel. FIG. 3A is a transistordiagram for one power MOSFET. In one example, the power MOSFETS areSTYGONM50 models from IXYS Corporation. It is also possible to useinsulated-gate bipolar transistors, other switching devices, diodes, orthe like, depending on the implementation. In the FIG. 3A power MOSFETexample, a body diode (or anti-parallel diode) DB provides afreewheeling path when the switches are off. The MOSFETS have a drain(D), gate (G) and source (S), and a threshold voltage VGS between thegate and source determines whether the MOSFETS are on and conducting oroff and not conducting. These gate circuits can be controlledprogrammatically by the controller 22.

Switch MI has its drain connected to a positive rail 36 and its sourceconnected to a high side 40 of the line filter. The high side of theline filter and a corresponding low side 42, correspond with the ACvoltage across the line voltage 16. Switch M2 has its drain connected tothe positive rail 36 and its source connected to the low side 42 of theline filter. Switch M3 has its drain connected to the high side voltage40 and its source connected a negative rail 38. Finally, switch M4 hasits drain connected to the low side voltage 42 and its source connectedto the negative rail 38. The gates of each switch MI-M4 receives acontrol signal (VGS1-VGS4, respectively) from the controller 22, whichmay be in the forms of pulse width modulation signals, to control whenthe switches are on or off.

FIG. 4 illustrates five signal diagrams, one of the input voltage (FIG.4A) to the bridge 20, and one for the control signals to each of theswitches MI-M4 (FIG. 4B, PWM control VGS1 for MI; FIG. 4C, PWM controlVGS2 for M2; FIG. 4 c, PWM control VGS3 for M3; and, FIG. 4E, PWMcontrol VGS4 for M4). The input voltage to the bridge, as shown in FIG.4A, is a 60 Hz wave form of 240VAC (RMS), with peak voltages ofapproximately positive 340 volts and negative 340 volts. Generallyspeaking, the bridge switches are synchronized with the line frequencyto provide a full wave rectified output. In one particularimplementation, the threshold voltage for each power MOSFET MI-M4 is2.4;hence, the PWM signal for each transistor switches betweenapproximately 12 volts and 0 volts at a 50% duty cycle. In this example,the 12 volt “on” voltage provides a margin of error above the thresholdvoltage to help avoid erroneous switch activation. The duty cycle isaligned with a zero crossing point of the line voltage and about a deadband, so that at or above 12 volts magnitude each switch is on andconducting, and below 12 volts magnitude each switch is off. To operateas a full wave rectifier and as shown in FIGS. 4B-4E, the controlsignals for switches MI and M4 are the same, and the control signals forswitches M2 and M3 are the same, with the control signals for each pairbetween approximately 180 degrees out of phase. Stated differently,switches MI and M4 are turned on, while switches M2 and M3 are off, andswitches MI and M4 are then turned on while switches MI and M4 areturned off.

To avoid having switches MI and M3 or M2 and M4 on and conducting at thesame time, the PWM control signals may provide a dead band between eachcontrol signal transition where all the control signal voltages are heldat 0 volts and hence all of the switches are momentarily off and notconducting. For example, there is a dead band 44 where all of thecontrol signals are at zero volts. Referring to FIGS. 4B-4E, the controlsignals VGS1 and VGS4 transition TI from 0 to 12 volts at the same time,while the control signals VGS2 and VGS3 transition T2 from 12 to 0 voltsat the same time. With respect to each of the illustrated first controlsignal transitions TI and T2, VGS1 and VGS4 are at zero volts whilecontrol signals VGS3 and VGS4 transition to zero volts. For a period oftime, the dead band 44, all control signals are zero volts. After thedead band, VGS1 and VGS4 transition (TI) to 12 volts while VGS3 and VGS4remain at 0 volts. In one example, the dead band for a 110/120VAC sourcevoltage is 300 microseconds and the dead band for a 220/240VAC sourcevoltage is 140 microseconds.

The bridge dead bands may be achieved in various ways. In one example, acomparator with some threshold voltage input, e.g., 9.1 Volts, iscompared to the line voltage. When the line voltage meets or falls belowthe threshold, whichever PWM signals are high (and hence the drivenswitches are conducting) are driven low to generate the dead band. Otherways of providing the dead band are also possible.

FIG. 4F illustrates one possible full wave rectified output between thepositive and negative rails (36, 38) of the bridge 20. The peak voltageis about 340 Volts, with an average DC value of 216 volts. Hence, theinput to the DC-to-DC converter stage 30 is a full wave rectified sinewave. In the case of a 100 VAC or 120 VAC line voltage, the peakvoltages are about 170 Volts and 160 volts, respectively.

Referring again to the charge configuration of FIG. 3, the DC-to-DCconverter 30, in one particular implementation, involves a boost circuit44 followed by a buck circuit 48, with a DC link 46 positioned betweenthe boost and buck circuits. The boost circuit amplifies or steps up thefull wave rectified voltage. In one example intended to charge a batterypack with about a 372 VDC (fully charged voltage), the boost stage isconfigured to produce about 400 Volts DC. The boost stage may include acapacitor C3 coupled between the positive rail 36 and the negative rail38, and in parallel with the output of the bridge 20. The boost circuitmay further include an inductor L2 in series with a diode D1. A controlswitch M5, which may be of the same form shown in FIG. 3A, is inparallel with the capacitor C3, and has its drain connected between theinductor L2 and the diode D2. The source of the control switch isconnected with the negative rail 38. The gate of the switch isconfigured to receive a control signal from the controller 22, which mayinclude a proportional integral (PI) controller and a PWM module. Due topotentially high current loads, the switch M5 may be realized by threepower MOSFETS connected in parallel.

FIG. 5 is a diagram illustrating a controller configuration 50 thatprovides a control signal to the boost switch M5. The controller 50 mayform a portion of the overall control 22. The controller includes a PIcontroller 52 providing a reference voltage to a PWM generator 54. ThePI controller receives as its input, a voltage signal representing thedifference between the output of the boost circuit, which is one exampleshould be 400 VDC, and reference voltage of 400 VDC. Hence, the PIcontroller receives an input voltage signal representing the differencebetween the actual output of the boost circuit 44 and the expectedoutput of the boost circuit. In turn, the PI controller provides areference signal to the PWM module 54 that drives a voltage signal tothe switch M5 in order to maintain the boost circuit output at thespecified voltage (e.g., 400 VDC).

In one particular boost circuit implementation, C3 has a value of 4.7uF, L2 has a value of 50 uH, and C4 (the link capacitor) is 2.16 mF. ThePWM signal may have a duty cycle range between 0 and 0.95, and the PIcontroller may be set at Kp=0.1 (the proportional gain multiplier of theerror input signal to the PI).

FIG. 6 illustrates various signal diagrams related to the boost circuit.More particularly, FIG. 6A illustrates the voltage output of the boostcircuit (the voltage output across the DC link capacitor 46). The boostcircuit output, with the parameters set forth herein, has a 400 VDCoutput with about 1V of ripple. FIG. 6B illustrates the current outputof the inductor L2 and FIG. 6C illustrates the voltage of the inductorL2. The boost inductor current shows that it is in continuous conductionmode with about 40% ripple current. It is also possible to implement theboost circuit as well as other circuits to operate in discontinuousconduction mode. FIGS. 6D illustrates the voltage level of the switch M5(between drain and source) for the PWM control signal to the gate of theswitch M5 as shown in FIG. 6E.

Hence, FIGS. 6A-6E collectively illustrate the function of the boostcircuit. When the switch M5 is on, under control of the circuit shown inFIG. 5, current from the capacitor C3 and rectifier circuit 20 areallowed to flow through the inductor L5 thereby charging the inductor tothe target voltage (e.g., 400 VDC). When switch M5 is closed, 400 VDC(shown in FIG. 6C) is available from the inductor L2 to charge capacitorC4 to 400 VDC (or to maintain the capacitor voltage at 400 VDC) as shownin FIG. 6A.

Besides the boost circuit controller 50, FIG. 5 also illustrates alimiter circuit 56 configured to shut off the switch M5 when the outputcurrent from the boost circuit meets or exceeds a current thresholdvalue or the output voltage of the boost circuit meets or exceeds avoltage threshold value. In one example, the limiter generates a controlsignal to turn off the switch when the output current of the boostcircuit exceeds 90 amps or the DC voltage of the boost circuit exceeds430 VDC. Other limiter threshold values are possible depending on theratings of various components (e.g., maximum electrolytic capacitor C4voltage, MOSFET current switching limitations, inductor L2characteristics), and any number of other possible factors (e.g.,overall maximum inverter-charger power conversion) that might effectcircuit performance.

In one particular implementation, the limiter 56 includes a NOR gate 58receiving as its inputs the results of two comparator circuits (60, 62).The first comparator 60 compares the output current of the boost circuit44 to a current threshold value (e.g., 90 A). The comparator provides adigital 0 output if the boost circuit is less than 90 A, and provides adigital 1 output if the boost circuit current is greater than 90 A. Theoutput of the comparator is fed into the NOR gate 58. Similarly, thesecond comparator 62 compares the boost circuit output voltage to avoltage threshold value (e.g., 420 VDC). The comparator provides adigital 0 output if the boost circuit voltage is less than 420 VDC, andprovides a digital 1 output if the boost circuit voltage is greater than420 VDC. The output of the second comparator 62 is also fed into the NORgate 58.

The NOR gate 58 provides a digital 1 when both inputs are digital 0,otherwise the NOR gate provides a digital 0 or low voltage output (oneor both inputs are digital 1). Thus, the NOR gate provides a logic 1signal to an OR gate 64 only when both inputs of the NOR gate are logic0, otherwise the NOR gates provide a logic 0 signal to the OR gate 64.The OR gate 64 receives as a second input, a protection input in theform of a digital 0 (logic 1 passing through an inverter (not gate) 66.Hence, the limiter provides a digital level I from the OR gate 64 to amultiplier 68 only when the boost current and voltage are below thethresholds. The multiplier also receives the PWM control signal thatdrives operation of the switch M5 as the second input to the multiplier.Thus, when either the inductor current of the boost circuit exceeds 90 Aor the output voltage of the boost circuit exceeds 420 VDC, the limitercircuit provides a logic 0 to the multiplier, which in turn drives thecontrol signal to the switch M5 low turning it off. When both the boostinductor current and output voltage are below the threshold values, thelimiter circuit provides a digital 1 to the multiplier 64, allowing thecontrol signal from the PWM 54 to pass through to the switch. Without alimiter circuit, the PWM is connected to the switch M5.

The output of the Boost/DC-Link provides a regulated DC voltage to thebuck stage 48. In the charge configuration shown in FIG. 3, the buckstage regulates battery charging by controlling the charge current tothe battery 14. The buck stage includes a switch M6 connected in serieswith the output of the boost circuit 44. An inductor L3 is coupledbetween a positive terminal of the battery 14 and the drain of theswitch M6. A diode D2 is connected between the inductor/switch junctionand the negative rail 38 of the inverter-charger. In one implementation,the inductor L3 has a value of 50 uH and the switch M6 is implementedwith three power MOSFETS coupled in parallel.

Generally speaking, when switch. M6 is on, the boost circuit and theDC-link capacitor source charging current to the inductor L3. Further,the diode D2 is reverse biased. When the switch M6 is off, diode D2 isforward biased and stored energy in the inductor provides a chargecurrent to the battery 14.

FIG. 7 is a diagram illustrating a controller configuration to controlthe operation of the buck circuit switch M6. While other implementationsare possible, in the control diagram depicted in FIG. 7, buck circuitcontrol involves a comparison between the buck circuit current output 72to the battery 14 and a reference current 70. The reference current maybe set at whatever the desired battery charging current. Further, thereference current level may be programmable. In one possible example,the reference current is 17 amps. A difference or error signal from asubtractor 74 (a difference between the actual current and the referencecurrent) is provided as in input to a PI controller 76, which provides areference voltage to a PWM generator 78. The PWM generator 78 providesPWM signal to the switch M5 thereby controlling the switch to therebycontrol the output charging current of the buck circuit.

FIG. 8 is a circuit diagram illustrating the inverter-charger 10 in adischarge (inverter) configuration. In the discharge configuration, thebattery 14 is coupled by way of the inverter-charger to the AC powersupply (e.g., a power grid, or load, etc.) 16, and the battery deliverspower to the source. Hence, in discharge mode, the battery may be usedas a source for alternating current power. In a smart grid application,for example, the battery can act as a storage mechanism to deliver powerback to the grid pursuant to any of a number of possible smart gridimplementations (off peak charging, peak load discharge; gridregulation; back up power supply for home; storage for wind or solarpower generation; etc.)

In the discharge configuration, the battery 14 is coupled with the DC-toDC converter mechanism 30. However, unlike the charge configurationwhere the buck circuit 40 (FIG. 3) is connected to the battery, thebattery is switched to being coupled with the boost circuit 36. Theboost circuit 36 provides a regulated DC voltage, higher than the packvoltage, in conjunction with the DC link 38, to the buck circuit 40. Thebuck circuit in turn provides proper current and voltage supply to thebridge 20 that, under PWM control, converts the output of the DC-to DCcircuit 30 to an AC waveform suitable for coupling to the AC source 16or for delivery directly to an AC load. For example, in the case of aconventional U.S. household outlet supply, the bridge provides a 60 Hz,120 VAC (RMS) output voltage or 240 VAC (RMS) output voltage which, forgrid tie applications, is precisely synchronized with the grid AC power.

Referring now in more detail to FIG. 8, the boost circuit 36 includesthe same components (L2, D1, C3 and M5) in the same configuration as theboost circuit 36 of FIG. 3. However, by way of some form of switchingmechanism, such as relays discussed in more detail with respect to FIG.12, the boost circuit 36 is switched to being coupled with the batterypack 14. More particularly, the capacitor C3 is connected in parallelwith the battery 14. The inductor L2, followed by the diode D1, areconnected in series to the positive side of the battery 14. The switchM5 is connected in parallel with the capacitor C3, with its drainconnected between the inductor and the diode, and its source connectedwith the negative rail 38.

For inversion, the boost stage 36 up converts the battery voltage to adirect current voltage sufficient to drive the rectifier with sufficientvoltage for coupling to the source. For example, in the case of a systemoptimized for a 240 VAC source, the boost circuit 46 increases thebattery voltage, which may be about 370 VDC to 400 VDC. The boostcircuit may be controlled in generally the same manner in discharge modeas in charge mode through using the circuit shown in FIG. 5, with thePWM providing a control signal to the switch M5. Generally speaking, thecontroller is configured to monitor the DC link voltage (i.e. thevoltage level of the boost circuit output) and through a feedback loopwith a reference voltage (400 VDC in this example), maintain the boostoutput voltage at 400 VDC.

The boost circuit provides a regulated up converted voltage to the buckcircuit 40. The buck circuit, in turn, provides an output signalappearing as a rectified sine wave input to the bridge 20. The buckcircuit 40 includes the same components M6, L3, and D2 discussed withreference to the buck circuit 40 in the inverter-charger charge modeconfiguration of FIG. 3. The switch M6 is operated to alternately allowcharging of the inductor, when the switch M6 is on, and allow dischargeof the inductor energy to the bridge when the switch is off.

FIG. 9 is a diagram of a controller for the buck circuit operating ininverter mode. The controller provides an output current (see FIG. 1 OC)to the bridge 20, with the output current having a dead band 94. First,to provide output current control of the buck circuit, the controllercompares actual output current 82 of the buck circuit (at inductor L3)with a full wave rectified line current reference 80. A subtractor 84provides the difference between the actual current and the referencecurrent to a PI controller 86, which provides a reference signal to PWM88.

Dead band control is provided by a comparator 92 that compares therectified line voltage (or the line voltage) to a threshold or offsetvalue above the zero crossing point of the line voltage. When the linevoltage falls between the offset value and the zero crossing, thecomparator provides a digital 0 output; otherwise the comparatorprovides a digital 1 output. A multiplier 90 receives the output of thecomparator 92 and the PWM control signal. The PWM signal is thusprovided to the switch M6 except during the dead band 94 providedthrough the dead band controller 92.

FIG. 10A illustrates the voltage output signal waveform of the buckcircuit 40 in inverter mode, with a 400 VDC input voltage to the buckcircuit for supplying the appropriate voltage waveform to a 240 VACline. FIG. 10B illustrates the buck circuit current output, with deadband 94, that drives the bridge 20. As can be seen, the output waveforms are in the form of a full wave rectified waveform. The bridgecircuit is controlled in the same way in discharge (inverter) mode as incharge mode, which is discussed herein with respect to FIG. 4. Theoutput of the rectifier is shown in FIG. 1 OC, and is in the form of a60 Hz 240 VAC (RMS) waveform.

FIG. 11 is a diagram illustrating one possible relay configuration forswitching between the charge mode configuration shown in FIG. 3 and theinverter mode configuration shown in FIG. 8. A set of relays 28 areprovided to alter the connection of the DC-to-DC conversion components30 between the battery 14 and the bridge 20. The diagram illustrates thefunctional connections achieved through any various possibleimplementation of relays. Relays or other forms of switches R1-R4 arepositioned to switch between the charge configuration and the inverterconfiguration upon receipt of a mode signal. In charge mode, the bridge20 is connected to the boost circuit through relays R1 and R4, and thebattery is connected to the buck circuit 48 through relays R1 and R3. Ininverter mode, the battery is connected to the boost circuit 44 throughrelays R1 and R3 and the buck circuit is connected to the bridge 20through relays R2 and R4.

Although the present invention has been described with respect toparticular apparatuses, configurations, components, systems and methodsof operation, it will be appreciated by those of ordinary skill in theart upon reading this disclosure that certain changes or modificationsto the embodiments and/or their operations, as described herein, may bemade without departing from the spirit or scope of the invention.Accordingly, the proper scope of the invention is defined by theappended claims. The various embodiments, operations, components andconfigurations disclosed herein are generally exemplary rather thanlimiting in scope.

The invention claimed is:
 1. An inverter charger for providing abi-directional energy flow between an alternating current source and adirect current chargeable voltage source, the inverter chargercomprising: an H-bridge rectifier inverter circuit coupled with analternating current voltage source; a direct current voltage to directcurrent voltage converter (DC-to-DC converter) comprising a boostcircuit and a buck circuit, coupled between the H-bridge rectifierinverter circuit and a direct current chargeable voltage source having adirect current voltage, the DC-to-DC converter switchable between acharge configuration and an inverter configuration; the chargeconfiguration including the boost circuit operably coupled with theH-bridge rectifier inverter circuit, the H-bridge rectifier invertercircuit providing a full wave rectified output signal to the boostcircuit, the boost circuit configured to up convert the full waverectified output signal, the charge configuration further including thebuck circuit operably coupled with the boost circuit, the buck circuitconfigured to provide a regulated charge current to the direct currentchargeable voltage source; the inverter configuration including theboost circuit operably coupled with the direct current chargeablevoltage source, the boost circuit configured to up convert the directcurrent voltage of the direct current chargeable voltage source, and thebuck circuit configured to provide a full wave rectified signal waveform to the H-bridge rectifier inverter circuit, the H-bridge rectifierinverter circuit configured to tie an alternating current voltagewaveform to the alternating current voltage source; and a plurality ofswitches configured to switch the DC-to-DC converter between the chargeconfiguration and the inverter configuration by: connecting an input ofthe boost circuit to the H-bridge rectifier circuit and an output of thebuck circuit to the direct current chargeable voltage source in thecharge configuration; and connecting the input of the boost circuit tothe direct current chargeable voltage source and the output of the buckcircuit to the H-bridge rectifier circuit in the inverter configuration.2. The inverter charger of claim 1 wherein the plurality of switchescomprise a plurality of relays.
 3. The inverter charger of claim 1wherein the H-bridge rectifier inverter circuit comprises four sets ofthree parallel connected power MOSFETS connected in a full wave H-bridgeconfiguration, with each MOSFET operating synchronously with thealternating current voltage source wave form to produce a full waverectified output of the alternating current voltage source.
 4. Theinverter charger of claim 1 further comprising control signals to theMOSFETS, wherein the control signals provide a dead band where allMOSFETS are off for a period of time around a zero crossing point of thealternating current voltage source.
 5. The inverter charger of claim 1wherein: the inverter charger further comprises a negative rail; theboost circuit comprises a first inductor and a first diode coupled inseries, and a first capacitor connected with the first inductor, theboost circuit further comprising a first switch connected between thefirst inductor and first diode, and the negative rail, the first switchin parallel with the first capacitor, the first switch receiving a firstcontrol signal to up convert the full wave rectified output signal whenthe inverter charger is in the charge configuration or to up convert thedirect current voltage of the direct current chargeable voltage sourcewhen the inverter charger is in the inverter configuration.
 6. Theinverter charger of claim 5 further comprising: a DC Link capacitor inparallel with the boost circuit; and a boost circuit controllercomprising a limiter circuit including a first comparator that generatesa first output value as function of whether a boost circuit currentoutput exceeds a maximum boost circuit current threshold and a secondcomparator that generates a second output value as a function of whetherthe up converted full wave rectified signal at the DC link capacitorexceeds a maximum boost circuit voltage threshold, wherein the limitercircuit causes the control signal to turn off the boost circuit switchwhen the first output value and/or the second output values indicatesthat the maximum boost circuit current and/or maximum boost circuitvoltage is met.
 7. The inverter charge of claim 1 wherein: the invertercharger further comprises a negative rail; the buck circuit comprises asecond switch in series with a second inductor, and a second diodeconnected between the second switch and the second inductor and thenegative rail; the second switch receiving a second control signal forgenerating a specified charge current output of the buck circuit in thecharge configuration; and the second switch receiving a third controlsignal for generating a rectified sine wave input current to the bridgein the inverter configuration.
 8. The inverter charger of claim 7wherein the third control signal includes a dead band.